Conventionally, a distance measuring apparatus has been put into practical use to measure the distance to a measuring target. The apparatus measures the distance to a measuring target based on optical detection of light selected from visible and invisible light. The distance measuring apparatus is provided on a vehicle, which is a movable body, for example, in order to measure the distance (relative distance) between another vehicle, which is a measuring target or the like, and a host vehicle (the distance measuring apparatus itself). The distance measuring apparatus offers information about the distance thus measured as driving support information to a driving support apparatus or the like, for example, for supporting avoidance of a collision with other vehicles.
There are known distance measuring apparatuses for optically measuring distance to a measuring target, which are described in Patent Document 1 and Patent Document 2.
The distance measuring apparatus described in Patent Document 1 has a light source for projecting light formed in a predetermined pattern having different wavelengths from each other onto a measuring target and picks up an image of a pattern of the light projected onto the measuring target in a different direction from the optical axis of the light source. The distance measuring apparatus measures the distance to the measuring target based on a change in the pattern of the projected light and the pattern of the light subjected to the image pickup. Thus, the distance measuring apparatus described in Patent Document 1 needs to have a light source for projecting onto the measuring target, light having sufficient intensity for enabling the image pickup. For this reason, when the distance measuring apparatus described in Patent Document 1 is provided on a vehicle, the light source is to project a light pattern having such an intensity as to enable the image pickup onto a measuring target, which is placed apart from the host vehicle by several tens to several hundreds meters in some cases. In other words, the quantity of the energy consumed by the light source cannot be disregarded.
On the other hand, Patent Document 2 discloses a distance measuring apparatus using no light source. The distance measuring apparatus includes two cameras, that is, a camera that is sensitive to a visible spectral range and a camera that is sensitive to an infrared spectral range. The cameras are disposed at a predetermined interval therebetween. The distance measuring apparatus measures the distance to an identical measuring target by applying a triangulation method to an image of the measuring target, which is picked up by the respective cameras. Thus, the distance measuring apparatus described in Patent Document 2 does not need a special light source. For this reason, the energy consumption is admittedly low. In order to maintain high precision in the measurement of the distance, it is indispensable to accurately maintain the predetermined interval between the two cameras, which is the basis of the triangulation method.